This invention is concerned primarily with aluminum alloy chains used for hoisting anchors used on ships. In the prior art, it is known to use nylon ropes or iron chains for this purpose. However, nylon ropes, while lightweight, do not function well with automatic reeling systems due to slippage, etc. Iron chains, while enabling the use of a sprocket reel for automatic hoisting of the anchor, are quite heavy, particularly when long chains are used. Aluminum chains generally are considered to lack sufficient strength for use as anchor chains. Accordingly, there exists a need for a strong aluminum alloy chain that would be lightweight and enable the use of a sprocket automatic reeling device for hoisting an anchor.
However, it is a well-known theorem that a chain is only as strong as its weakest link. With aluminum chains, the problem encountered in manufacturing a uniformly strong chain is creating uniformly strong welds in every single link of the chain, which is normally manufactured by forming a loop of aluminum alloy rod stock with the ends of the loop unconnected, and then fusion welding the ends of the loop together using any appropriate fusion welding process. Due to the large number of links that normally constitute a chain, it is quite difficult normally in a manufacturing process to obtain an optimum weld for each weld in the links. Essentially, it was previously virtually impossible to detect by visual inspection whether or not sufficient weld penetration of the base metal occurred during any weld so as to ensure optimum strength for the particular weld being inspected. That is, a poor weld would appear visually just as acceptable as a very strong weld.
It is therefore highly desirable to provide a system for welding aluminum alloy chain links in a manner that will permit simple visual inspection to determine if adequate weld penetration of the base metal has occurred to thereby produce a weld that is at least as strong from a tensile strength standpoint as the base metal.